L.I. Bezruk

Improved gas-discharge etching techniques in the electron microscope study of polyamide structure☆

ACCORDING to establ ished views, fibrils, spherulites and single crystals are typica l supermolecular structures of polyamides. Fibr i l lar structures mainly characterize oriented systems [1, 2]. Xray diffraction a t low angles reveals a fairly strict al ternation of ordered and disordered regions along the fibrils [3], which is confirmed by an electron microscopic method of negative contrast [4] and are known as long periods. For polyamides they are within the range of 70-700 •, according to the chemical nature and t rea tment conditions of samples. Polyamide spherulites are large (up to several microns) formations with fibrils growing in a radial direction from the spherulite centre. They normally characterize crystallized, non-oriented systems. Up to recently single crystals were.considered as unlikely structural forms of polyamides since they can only be formed with unbranched polyamides and under certain conditions of crystall ization. For the same reason i t is difficult to imagine the simultaneous coexistence in the polymer of two crystalline morphological forms--single crystals and spherulites. The aim of this s tudy was to use etching with active oxygen (EAO) obtained in a field of a.c., linear, electrodeless, high-frequency discharge to examine the supermolecular structure of polyamide materials. Wi th most methods of electron microscope investigation used up to now, model polymer films have been used obtained under special conditions. We sought to observe s t ructural detai ls in industr ial polymer samples using EAO combined with the replica method. The use of chemical etching to reveal the supermolecular structure of polyamides does not enable the rate of etching to be controlled to the required extent and almost inevi tably causes s tructural variat ions in the surface layers of the polymer. The use of cathode sputtering (ion bombardment in plasma of high-voltage d.c. discharge) results in considerable heating of the polymer surface layer by absorption of par t of the electronic plasma component mainly consisting of fast electrons and recombination of electrons and ions in the polymer. The use of EAO based both on the effect of ionic polymer bombardment and the action of act ivated oxygen, apparent ly consisting of neutral atoms and gas molecules, in burning

Methods of investigation electron microscope study of the structure of polymeric materials

Abstract The effect of the morphology of supermolecular formations in polymers on their physical and mechanical properties is now well known [1]. Up to now, in most studies concerning the electron microscope investigation of a supermolecular structures in polymers the specimens were prepared in the form of ultra-thin polymer films from solution either by shearing or mechanical crushing. Determining the structures in bulk polymers has considerable practical importance. This paper deals with the electron microscope study of these structures. For this purpose we developed new methods of etching polymer surfaces to study the structure of polymer products (fibres, films, units and friction surfaces).

The structure of segmented polyurethanoureilenes

Abstract The structure of polyurethane block copolymers (segmented polyurethanes) has been investigated by low angle X-ray diffraction and electron microscopy. It was found that substitution of a polar for a non-polar substituent in the side group of the chain of a rigid block causes separation into phases of different density on the microscopic.

Morphological evaluation of changes in the supercrystallite structure of two component polymer mixture obtained from melt

Abstract An investigating the morphology of incompatible polymer mixtures it was shown that the homogeneity of supermolecular structures observed using the electron microscope, is not evidence of compatibility on a supermolecular level, but is merely the result of a weak optical contrast. Individual morphological structures can be detected in these systems by transfer to the oriented state. Separation into two clearly expressed phases in this case distinctly indicates the absence of compatible supermolecular structures. When an intermediate layer is formed at the interface, this is a typical sign of morphologically incompatible polymers.

X-ray study of microheterogeneity of polyethylene and polyoxymethylene melts☆

Abstract Results are described of an X-ray study of low pressure PE-POM and high pressure PE-POM polymer mixtures, in order to obtain microheterogeneous structural characteristics. A statistical analysis of results, in comparison with results of model calculations, indicates that a model of microheterogeneous structure corresponding to the thickness of boundary layer of POM not exceeding 50–100 A and dimensions of inclusions of the order of 0·2-0·4 μm, is the most suitable.

A possibility of observing the structure forming process in polypropylene crystallization

The existence of the specific metastable phase made it possible to carry out multistage electron microscopic investigation of the supermolecular structure formation in the crystallization of polypropylene in the oriented state. Comparison with the data of electron diffraction yielded a direct evidence of the fact that the formation of structural units of the supermolecular organization of crystalline PP, i.e. fibrils and lamellae, occurs in the stage of orientation, and crystallization itself only fixes these structures. Die Existenz einer spezifischen metastabilen Phase erlaubt es, mehrstufige elektronenmikroskopische Untersuchungen der Bildung der ubermolekularen Struktur bei der Kristallisation von Polypropylen im orientierten Zustand durch zufuhren. Der Vergleich mit Elektronenbeugungsaufnahmen liefert einen direkten Beweis dafur, das die Bildung von Struktureinheiten der ubermolekularen Ordnung im kristallinen Polypropylen, d. h. der Fibrillen und Lamellen, wahrend der Orientierung erfolgt und die Kristallisation diese Strukturen nur fixiert.

On the Character of Failure of Adhesive Joints Between Two Polymers

Abstract Up to the present there has been discussion of the locus of fracture of adhesive joints, i.e., if it proceeds precisely at the interphase border, or if cohesive fracture in a weak layer of one of the components takes place. There are only a few data available on this point.

Separation of replicas from the polymer surface etched in oxygen plasma

Abstract To facilitate the separation of replicas, the polymer surface was passivated after etching by prolonged retention in butyl and isobutyl alcohol and repeated brief action of the plasma on the sample with the replica on it.

A note on microfibrils in polyethylene

Abstract The results of diffraction (low-angle scattering of X-rays and electrons) and electron microscopy study show a significant qualitative coincidence in studies of the morphology of oriented polyethylene films obtained from polyethylene single crystal mats. The morphology approximates the ideal description of a microfibrillar structure. In certain cases a quantitative coincidence of the periods of alternation of densities along and across the texture (when comparing visible images and average periodicity from the data of X-ray diffraction study) is also obtained.